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Equine arteritis virus (EAV) belongs to the family Arteriviridae of the order Nidovirales. The viral genome composed by single-stranded positive sense RNA is enclosed in a icosahedral nucleocapsid and surrounded by a proteolipid envelope. The genome consists of nine open reading frames (ORFs) coding both structural and non-structural proteins. Although only one serotype of EAV is distinguished, field isolates differ in virulence and pathogenicity. The EAV infection is usually subclinical. 30-60% of stallions after infection become persistent carriers of the virus and can shed EAV with their semen during next several weeks, months or even years. Mares covered by EAV shedding stallions can result in abortions, fetus resorptions, infertility and even death of the newborn foals that lead to large losses in horse breeding. Seropositive stallions sheding the virus in their semen are the main reservoir of the virus; the control of the disease, therefore, should be based on their identification and elimination from breeding. Genetic variability of EAV can lead to the increase of virulence of the isolates and to changes in viral properties having an impact on the results of laboratory testing. Researching genetic modification of the viral genome provides important information about the changes in the nucleotide sequence of currently circulating strains and about the direction of EAV evolution. The purpose of the review is to present current data concerning molecular biology and diagnostics of equine arteritis virus infections.
The purpose of the study was to analyse the genetic diversity of Polish EAV isolates. Genetic variability can lead to increased virulence of isolates and to significant changes in EAV antigen properties influencing the results of laboratory testing. Studies on genetic modifications of viral genomes as well as on the phylogenetic affinity of strains have facilitated the investigation of viral evolution. Phylogenetic analysis was performed on 32 isolates that were isolated from the semen of asymptomatic virus-shedding stallions originating from 8 national studs. These isolates were compared with 15 reference EAV strains commonly used in phylogenesis. On the basis of the nucleotide sequence analysis of ORF5 gene encoding GP5 glycoprotein it was shown that Polish EAV isolates belonged to two subgroups and demonstrated the closest relationship to the European strains. None of these strains had any relationship to the first Polish strain Wroclaw-2 isolated in 1976. The homology of ORF5 nucleotide and predicted GP5 amino-acid sequences of Polish isolates attained a level of 81.2-99.0% and 90.1-99.4% respectively. Analyzing the genetic diversity of ORF5 facilitated the conducting of retrospective epizootic investigations.
In the study flow cytometry was attempted to identify EAV infection in stallions’ semen. Material for the study consisted of 8 semen samples taken from EAV-seropositive stallions. The samples were put on RK-13 and Vero cells. After a 24-hour incubation period the cells were treated with a specific conjugate and then analyzed in FACS aparatus. In the case of two samples positive fluorescence was observed. The above positive result was confirmed by virus isolation in both cell cultures used.
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